[96.05] Engines and Ejecta of Gamma-ray Bursts

S. R. Kulkarni (Caltech)

The BeppoSAX era saw the discovery of afterglow emission
from long duration GRB s. The resulting X-ray, optical and
radio studies of the afterglow emission conclusively linked
long duration gamma-ray bursts with deaths of massive stars.
Thanks to Swift and HETE we now know that short hard bursts
do not have associated supernovae and can be found in
elliptical galaxies. The stage is now set to start
understanding the physics of the explosions. I consider and
address the following two questions: (1) is the central
engines active for a long time (relative to the burst)? (2)
what are the physical parameters (mass, velocity and
composition) of the ejecta? The rapid as well as sustained
response by the XRT aboard Swift and the resulting
panchromatic studies with ground based facilities allow
these questions to be now addressed.